Plastisols and organosols are well known to those skilled in the art. Thus, a plastisol is a suspension of a finely divided hompolymer or copolymer of vinyl chloride in one or more liquid plasticizers which have little or no tendency to dissolve the resin at ambient temperatures but which becomes a solvent for the resin upon being heated. Organosols are similar to plastisols with the exception that they also contain about 5% or more of one or more volatile diluents and dispersants. At elevated temperatures the vinyl chloride resin is completely dissolved in the plasticizers, forming an essentially homogeneous plastic mass which upon cooling is in the form of a substantially flexible solid. Additives such as fillers, antioxidants, stabilizers and colorants are also usually present in these formulations. Plastisols are conveniently utilized in a wide variety of processes in the plastics industry including rotational molding, slush molding, dipping, spraying, film casting and coating while organosols are used primarily in spread coating applications as well as in some spray and dip coating applications.
A procedure which is often employed in the compounding of plastisols and organosols involves the admixture of a dispersion resin with an extender or blending resin. Dispersion resins are vinyl chloride homopolymers or copolymers which can have a very small particle size in the range of about 0.1 to 3.0 microns which permits them, after suitable processing such, for example, as by grinding, to be mixed with plasticizers by simple stirring techniques. Such dispersions are often diluted with extender resins which are usually prepared by suspension polymerization processes and which have substantially larger particle sizes in the range of from about 5 to 60 microns. In addition to reducing costs, the partial replacement of dispersion resins with extender or "suspension" resins also serves to alter certain properties of the resulting plastisol of organosol resin blend.
The preparation of plastisols or organosols containing these blends of dispersion and extender resins often presents many processing problems to the practitioner because of the mechanical difficulties and material handling operations involved in preparing a homogeneous blend of two dry particulate materials whose respective particle sizes differ substantially from one another. In addition, the extender and dispersion resins must each be subjected to separate drying operations prior to being blended. And, in the case of the dispersion resin particles, upon being spray dried prior to being dispersed in a plasticizer, they will ordinarily agglomerate into clumps having a diameter of up to about 100 microns which necessitates, as noted above, the grinding of the resulting agglomerated resin so as to reduce these agglomerates to a more suitable particle size. This is necessary as the agglomerate will not otherwise disperse. Moreover, since the final blending operation of the dispersion and extender resins within a plasticizer is ordinarily carried out by the customer or ultimate user of the resins rather than by their manufacturer, the user is required to maintain an inventory of both the extender and dispersion resins.
Thus, it is the prime object of this invention to utilize an improved procedure to prepare blends of dispersion and extender resins displaying unique physical and rheological properties. It is a further object of this invention to prepare these unique blends by means of a novel process which substantially eliminates the various mechanical difficulties and handling operations which are presently involved in their preparation. Various other objectives and advantages of this invention will be apparent from the disclosure which follows hereinafter.